basically they just cut the old water neck off and braze on the new one in the correct size and then moving the water neck is a process of cut and braze in new location and then fill in/braze where old water neck was. Like noted I think a lot of the people are plastic tank types now and they don't even deal with the old school things...ie brass tanks. New way is to just buy another plastic tank and see how long until the next replacement. Allthough I will say I've had good luck with the radiators on my GM pickups...non-issue..but basically when they have a problem you just get a new one...no real repair work.